December 9, 2004
01:00 PM (EST)

News Release Number: STScI-2004-33

Spitzer and Hubble Capture Evolving Planetary Systems

December 9, 2004: Two of NASA's Great Observatories, the Spitzer Space Telescope and the
Hubble Space Telescope, have provided astronomers an unprecedented look
at dusty planetary debris around stars the size of our sun. Spitzer has
discovered for the first time dusty discs around mature, sun-like stars
known to have planets. Hubble captured the most detailed image ever of a
brighter disc circling a much younger sun-like star. The findings offer
"snapshots" of the process by which our own solar system evolved, from
its dusty and chaotic beginnings to its more settled present-day state.

Debris disks are composed of the shattered remnants of small bodies such
as comets and asteroids that collided as they orbited the star. A
similar, though much less dense cloud of dust orbits our Sun. Large,
gaseous planets like Jupiter might already exist in such systems,
while much smaller rocky planets like the Earth may be just starting to
form.

Q & A: Understanding the Discovery

1.
Why do stars have disks?

When a star forms through the collapse of a huge cloud of gas and dust,
some of the material will settle into a flattened disk around the star
that is at a right angle to the star's spin axis. This material has
maximum centripetal force along this plane and so resists falling into
the star. The disk eventually dissipates after the star ignites. But
before it does, planets, asteroids, and comets may agglomerate from dust
sticking together in the disk. A secondary disk forms when the smaller
bodies collide and grind each other back down to dust.

2.
Do all stars have debris disks?

NASA's Spitzer Space Telescope has detected the telltale infrared glow of
excess dust around a number of young stars. However, some stars appear
to lose material too early to make planets. What's new is that some of
the stars with debris disks have planets, as identified in previous studies.
These planets have never been directly seen but identified through the
telltale gravitational wobble they induce on the star. The new Spitzer
observations are the first direct link between existing extrasolar planets
and circumstellar disks.

3.
Does our Sun have a debris disk?

Secondary disks around young stars are very dusty due to a spate of violent
collisions. Our solar system is somewhat middle-aged, and the rate of
collisions has died down dramatically. Still, the ecliptic plane of our
solar system, where all the major planets and asteroids lie, has about
one ten-thousandth as much dust as seen around young stars. This can be seen
from Earth as a thin pillar of faint light in the night sky called the Zodiacal
Light. It is best seen from the tropics where the ecliptic is typically at a
steep vertical angle to the horizon.